Lately, a high density is promoted in a semiconductor mounting technology to realize high functionality, enhanced performance, and downsizing of electronic devices. A wire bonding (WB) technology, a tape automated wire bonding (TAB) technology relating to a wireless bonding technology, and a flip chip bonding (FCB) technology are listed as a representative technology of bonding method for bonding semiconductor devices, as well as a semiconductor device and a circuit board. As the technology to mount in high density semiconductor devices such as computer, the flip chip bonding (FCB) technology enabling the highest density mounting has been widely applied. The flip chip bonding bonds bumps (protruding part) formed on the semiconductor device or the like to the circuit board or the like. The bumps are formed mainly by means of plating process. According to the plating process for forming bumps, it is possible to form finely patterned bumps. In addition, the height of the bump is intended to be controlled under the various conditions. However, there is a problem in which the height of the bumps is varied to some extent. As the remedy for the variation of the height of the bumps so as to prevent the contact failure of the electrode, the pressure is applied at the bonding in order to closely contact all the bumps. The above described method is possible, however, the excessively applied pressure causes the strain to remain within the bump, and lowers the thermal stress resistance to result in the breakage. Accordingly, the structure of the bump for connecting to the metal fine pattern has preferably soft and flexible structure when the pressure is applied.
In addition, the bump formed by means of the plating has a problem in which cracks and fractures are caused supposedly due to the fatigue failure in the process of the usage. In the flip chip bonding (FCB) technology, in case that the material forming the semiconductor device is different from the material forming the circuit wiring board, the stress strain is caused on the solder bump electrode due to the difference of the expansion coefficients. The above described stress strain damages the solder bump electrode to lower a reliable life time. As the means to solve the above described problem, a porous body is known, which is formed by sintering the conductive paste containing metal fine particles.
Patent document 1 discloses, as the connecting bump for electrically connecting the conductive wiring circuit and the substrate, the bump comprising porous metal formed by sintering the metal fine particles having the mean particle diameter from 0.1 μm to 50 μm and the density thereof is from 0.2 to 0.9 times of that of the bulk type metal. Patent document 2 proposes the bump formed by a sintered porous body having elasticity and relatively soft. Since the bump has elasticity, even though the height of the bumps varies, the porous body is contracted by the applied pressure so as to enable the bonding. In addition, a lesser strain remains within the body, thus preventing to lower the heat resistant stress. Patent document 3 discloses a bonding process in which a porous metal layer comprising a third metal is interposed between the first metal layer and the second metal layer; a metal nano-paste, in which super fine metal particles having mean particle diameter up to 100 nm are dispersed in an organic solvent, is interposed between the first metal layer and the porous metal layer, between the second metal layer and the porous metal layer, respectively; and then the heating treatment is implemented to be bonded. Patent document 4 discloses bumps comprising a Au plating layer provided in a fine hole of a photo resist layer formed on a substrate (first bump layer, height of 10 μm) and a sintered body (a second bump layer) provided on the Au layer, in which Au paste as a metal paste is fallen as a drop and filled, and then sintered to form the sintered body. Patent document 5 discloses a method of manufacturing a ferrite porous body in which a sublimation substance is fully dissolved into an organic solvent, thus prepared dissolved liquid is blown from fine holes into water to precipitate fine particles of the sublimation substance, then thus obtained fine particles are mixed with a ferrite powder, then formed and baked.